1. Field of the Invention
The present invention relates to a process for uniformly charging an image holding member, and more particularly to a process for performing, in an image forming apparatus comprising an image holding member to be driven at two different speeds, the electrostatic charging of said image holding member in relation to the speed thereof, thereby realizing a uniform potential thereon. Said image holding member includes a photosensitive drum, an insulating drum, a transfer sheet material, a recording sheet material etc.
2. Description of the Prior Art
An image forming apparatus comprising an image holding member to be driven at two different speeds is already known and disclosed for example in the U.S. Pat. No. 4,044,671. In such apparatus the image holding member, for example composed of a photosensitive drum, is rotated at a first speed in the step of forming a first latent image thereon, while it is driven at a second speed at a subsequent step of transferring said first latent image onto another member or of forming a second latent image corresponding to said first latent image on another member by means of ion modulation, thereby obtaining a reproduced image.
In case a corona discharger is employed for obtaining a uniform potential on an image holding member having a changeable speed as explained above, there is proposed a process of changing the intensity of corona discharge in response to the speed of said image holding member in order to prevent significant fluctuation in the charged potential resulting from the speed change. However if the discharge intensity of the corona discharger is changed simultaneously with the speed change-over as has been usually conducted, there will result an abnormally charged portion in the boundary area of said change-over (area located directly under the discharger at said change-over) even if the discharge intensity is maintained constant after said change-over. Such abnormally charged portion becomes visible on the final image or results in an unnecessary carry-over of the developer material.
The analysis on this drawback has revealed that it is generated from the difference between the start-up speed state of the image holding member and the start-up state of the change of corona discharge. More specifically the image holding member, which is mechanically accelerated or decelerated from the first speed to the second for example by the change of motor pole number or by a transmission, will receive excessive or deficient corona discharge, the intensity of corona discharge is increased or decreased before the speed of the image holding member is stabilized to the new value, until said speed is thus stabilized.